1. Field of the Invention
The present invention relates to the treatment of mineral fiber or glass based waste, in particular glass fibers, contaminated with an organic substance to recover the vitreous material substantially free of organic substance, and use it as cullet in glass melting furnaces.
2. Discussion of the Background
The waste of mineral fiber and glass products containing organic materials poses disposal problems, not only due to their volume, but also due to the pollution they cause. For example, some mineral fiber binders used are formaldehyde, phenol and urea resins comprising free formaldehyde and phenol. These are hazardous, toxic substances subject to strict pollution control regulations. Furthermore, the vitreous material contained in this waste is an expensive product which is useful to recover.
It is usual to use ground waste glass, known as cullet, as a base material introduced into a melting furnace for the manufacture of glass. This waste glass serves in particular to assist the fusion of the other basic materials.
A problem arises when it is desired to use as cullet glass waste treated with a synthetic resin or mineral fiber waste used in insulating products contaminated with an organic substance serving as the binder thereof because these binders are generally phenoplast resins (formaldehyde--phenol--urea resins) or aminoplast resins (formaldehyde--urea--melamine resins). When this waste is melted in a conventional furnace, a low quality glass is obtained which has certain defects preventing its use as a base material in the manufacture of high quality glass (low energy transmission in the furnaces, tendency to form foam owing to the simultaneous presence of both reduced and oxidized vitreous materials).
Thus, the presence of organic contaminants in the waste glass fibers means that large quantities of oxidizing agents, such as sodium sulfate, have to be introduced in to the melting furnace. This causes SO.sub.2 to be given off in amounts greater than current pollution standards allow. These standards are likely to become even more restrictive in the future.